The rapid depletion and the increased usage of the world's petroleum supplies is changing the economics of energy storage and energy conversion systems. Use of solar energy is becoming fashionable and economical for water heating and home heating. Use of solar energy for domestic electricity is imminent.
Aqueous-acid solutions such as sulphuric acid solutions have long been known to release heat as the solution is further diluted with water. Also it is well known that distilling a dilute acid-water solution vaporizes water (working fluid) thus making the remaining solution more concentrated with acid (absorbent). Since the heat of solution or absorption is a significant amount of energy per unit weight of solution, chemical energy can be used for thermal energy storage. At least one U.S. Department of Energy program is concerned with the use of sulphuric acid-water solutions as a means to store thermal energy and chemical energy to produce a refrigeration-heating effect..sup.1 This program does not consider nor include conversion of available thermodynamic energy of the working fluid for the production of shaft power, nor does the disclosure include a discharge mode which uses thermal and chemical energy available in the concentrated solution to vaporize the working fluid held in the receiver. FNT .sup.1 Paper presented at ASME Annual Meeting 1978, Energy Storage Session, entitled "Sulfuric Acid-Water Chemical Heat Pump/Energy Storage System Demonstration" by E. Charles Clark, Rocket Research Company, Redmond, Wash. and Carl C. Hiller, Sandia Laboratories, Livermore, Ca.
A Swedish heat storage system is described in the November 1980 issue of Popular Science Magazine.sup.2 which uses water as the working fluid and sodium sulphite as the absorbent for the solution. This system uses solar energy to charge the system and an underground heat exchange loop for heat sink during charging and as heat source for discharging. Use of the available thermodynamic energy for conversion to shaft power is not described or suggested. FNT .sup.2 "Double Duty Heat Pump" by David Scott, pps 56-62, Popular Science Magazine, November 1980, Volume 217, No. 5.
This invention provides for economical storage of thermal energy and for conversion of a portion of the thermal energy to shaft power which can in turn be used to generate electricity or mechanical refrigeration. Heat rejected from the system may be useful for domestic heating, water heating, or the like. A unique feature of this invention is that power conversion is provided during the daylight charging cycle of the system and during the non-daylight discharging cycle of the system. The energy supply for the discharging cycle is stored as sensible thermal energy and chemical energy in the solution contained in the holding tank.